Physical modeling and UVP monitoring yield an efficient protection of a lake reedbed from erosion

The Lake Geneva revitalisation program includes among various measures the implementing of reedbeds along the artificialized riprap shoreline. The vegetation and its substratum must be protected against wind induced harms due to wave energy and currents. Since embankment-dikes in Suisse lakes are not permitted, according to the Suisse Federal Act on the Protection of Waters (RS 814.20), the Laboratory for Applied Hydraulics (LHA) of HEPIA has been mandated by the Service du lac, de la renaturation des cours d'eau et de la pêche of Geneva to carry out a detailed analysis by physical modelling of a double vertical-wall breakwater structure. The metal-wood structure designed by CERA civil engineers had to be optimized at the LHA, to achieve high wave-energy dissipation. In an experimental wave tank of the LHA, reedbed resistance and its substratum erosion potential were tested under 50-year return period wind conditions. The structural strains were also determined, under 100-year return period wind. The breakwater developed at the LHA prevents efficiently the reedbed against wind-wave induced harms and substratum erosion, as verified by Met-Flow UVP probes and described in the present study.